Two of a Kind
by WhisperingVoid
Summary: What if Percy had a sister? A twin in fact. Thessea and Percy Jackson come from the same mother and father, but don't know of each other. At least not yet. Very briefly dealing with the first five book. The story really kicks off with The Lost Hero.
1. Chapter I

**So I did decide to do the main story and as this being my first story, I hope all goes well. My plan isn't to retell the whole series, but just to add and change little things. So I won't really spend so much time with the first five books, but more with **_**The Heroes of **_**_Olympus_. Enough time wasted, let's get on with it, but first I don't own Percy Jackson and all that jazz, I just own my OC.**

Thessea was awakened by someone in the middle of the night. She groaned as she rubbed her eyes.

"This better be good."

"Tess, it's him. He's here," Annabeth spoke softly.

It took about a minute for Tess to figure out who 'he' was, but when she did she shot out of bed.

"Is he ok? It's the middle of the night," she rambled. Annabeth put her hand up to stop her.

"He's fine. He's in the infirmary."

Thessea seemed to relax as she lay back down.

"So when can I meet him?" she asked.

"Not until Chiron says so," Annabeth answered hesitantly.

"What?!"

"Not my choice, he said it'll give him time to adjust a bit before hitting him with the 'Oh you have sister that you were separated from since birth'"

Thessea groaned and pulled the covers over her head. "Fine."

Annabeth grinned at her friend before leaving for her own cabin.

* * *

Thessea stayed in the arena practicing her skills, occasionally glancing at Annabeth who stood beside Chiron and Mr. D. Thessea could scream at the gods for the emotions she was feeling.

"That dummy doesn't stand a chance," someone joked. Her dummy wasn't even touched a hair. She had too much on her mind to focus. Thessea glanced over at Annabeth to see she was advancing toward her.

"Well?" Tess asked.

"I'm going to check on his bunk in Hermes' cabin."

"What did he say?"

"He didn't say anything… I'm sorry, maybe later right?"

Thessea swallowed the pain and tried to smile and believe it would happen today.

She wandered the camp and eventually found her way to her cabin. The sad feeling in there was one of the reasons why she rarely went in there. She looked at the bunks and frowned.

"Oh, I wouldn't do that!" She heard Chiron warn and immediately jumped behind the door. She caught a glimpse of black hair as he stood in the doorway for a few seconds before being lead out.

"Come along, Percy."

It took everything in her to keep still. She waited before she was sure it was clear before letting out a restrained breath. The wait was killing her. Thessea basically lounged around in the cabin until dinner, which then she walked out alone. She hated dinner the most. Every other cabin had people to talk to and share laughs while she sat alone at a cold empty table. She, like everyone else carried her plate to the fire and pushed off a piece of her brisket and muttered "Poseidon." Thessea felt a pair of eyes on her and when she looked up she saw intense green eyes, matching her own. The staring contest was broken by Luke pulling Percy back to the table, but not before giving her his signature disappointed look. She heard Mr. D begin to speak,

"Yes, I suppose I'd better say hello to all you brats. Well, hello. Our activities director, Chiron, says the next capture the flag is Friday. Cabin five presently holds the laurels."

A huge roar of applause from the Ares table.

"Personally," Mr. D continued, "I couldn't care less, but congratulations. Also, I should tell you that we have a new camper today. Peter Johnson."

Thessea smiled in her glass as he was corrected.

"Er, Percy Jackson," Mr. D corrected. "Thats right. Hurrah, and all that. Now run along to your silly campfire. Go on."

Thessea spent most of the time at the amphitheater, looking for the same green eyes and she did right before the show was over. Apparently both of them had the same idea because they shuffled through the crowd to get closer. And when they did they said the same thing,

"I know you."

**Well here it is, the first chapter. I hope you like it and I'll try and make the next chapters longer and I guess more packed. Please review and tell me what you think, or if you have any thoughts, ideas, or opinions. Until next time.**


	2. Chapter II

**Not gonna say much here… except I don't own Percy Jackson and the Olympians and all that, they belong to Rick Riordan... Let's get to it.**

Thessea and Percy stood in front of one another, examining each other.

"I know I've seen you before." Percy stated.

Of course Thessea knew who he was, or knew of him was a better phrase. But as she stood there in front of him, memories started to resurface. It was just him and her still at the amphitheater, everyone else had cleared out.

"A few years ago, you were talking to my mom." Percy started. "She was crying when she saw you, happy tears."

"I remember that, you were just coming home or something, she was hugging me and you came in the room, the biggest stare down of my life," Tess chuckled.

"She wouldn't answer me when I asked who you were; instead she led you out the door. She acted as if she hadn't seen you in years-"

Thessea watched him as he finally connected the dots. She shifted from foot to foot before he finally said it, "You're my sister aren't you?"

Thessea nodded slowly, all the times she caught glimpses of him in her life and she's just now meeting him 'formally'. "The name's Thessea."

"I have a sister," Percy muttered, getting used to the taste of the word.

"Chiron and mom agreed to have us separated because of our scent. They figured if we were kept together we would draw to much attention. So he took me and she kept you."

"Wait, you know who our dad is?" he asked curiously.

"That is one thing I can't tell you. But I do have a question for you."

"What?"

"Where is mom? You came in the middle of the night and were thrown into the sick room. Is she ok?"

Percy clenched and unclenched his fists as he fought the tears, "She uh- the Minotaur- she's gone." That was all he could say.

Thessea felt bad for asking, and for Percy. She couldn't imagine what it felt like to see that happen, "I'm sorry."

Percy brushed it off and looked at the ground.

"I'll let you get to sleep," she whispered.

Thessea could never imagine what it would be like to be suddenly thrown into the world where gods and monsters exist. For her she grew up with it so it was nothing to her. Percy got to live with their mother, she dreamed everyday what it could've been like to be with her, if Chiron took him instead of her.

"What do you think?"

Thessea turned around to see Chiron stroll over to her. She shook her head slowly before opening her mouth, "Why?"

"Why what?" Chiron asked confused.

"Why'd you choose me instead of him?"

"Does it matter? I picked one to help your mother."

"But not him?"

"Thessea go to bed."

"But-"

"But nothing, go to bed now. This conversation is done," Chiron said sternly.

Tess opened her mouth to say something, but decided against it. She made her way to her cabin, thinking about the last time Chiron spoke to her like that.

* * *

Thessea stood in the training ring as she watched Percy wander around the camp. She just finished tying her bracers before activating her sword. It was fashioned like a ring, but became a sword when she twisted it. Her movements were fluid and graceful that she found it kind of silly that she still had to practice at times.

"Mind a sparring buddy?"

Thessea stopped mid-swing. She didn't even have to turn to see who it was.

"Sure Luke, ready to get your butt whooped?"

Luke just smirked as he gave a glance to his buddy, around the ring, spectating.

Luke gave no warning of an attack, causing Tess to dodge it quickly. She only had a second to parry his next attack before she followed it with a kick to his chest.

"Trying to kill me?" She shouted.

"Not at all." He said sarcastically.

Thessea took a jab just for him to side-step and kick her to her knees.

"Give up Jackson?" He asked.

"Never in your life Castellan!" Thessea hit him with the butt of her blade before sweeping his legs from under him. She planted her foot on his chest after kicking away his sword as she held her own blade to his neck. Luke's friend 'oohed' at the scene and began laughing. Thessea twisted the hilt of her blade, turning it back into a ring and held her hand out for him. Luke ignored it and got up himself.

"Fine, be like that," She muttered under her breath. Luke shot her a look before walking away with his friends.

* * *

Later that day she saw Percy in the ring with Luke and silently prayed to her father he wouldn't get pummeled. She was actually surprised that he was holding his own, and managed to disarm him on his first try. _Must run in our blood_ she thought with a smile. Tess caught up with Annabeth to discuss and trade tactics for Capture the Flag. They discussed for awhile, chatted about other things before it was time to get set up.

"Does Athena have a plan?" Thessea asked before putting on her gear.

"Athena always has a plan," Annabeth smiled.

The pair watched their team get situated and fit with armor.

"Luke's gonna try and kill me," Tess whispered to Annabeth.

"That's crazy. Luke wouldn't do that," the blonde answered.

"He's still mad."

"From five years ago?"

Tess nodded slowly, "He still thinks it's my fault.

The two girls stood in silence before Annabeth opened her mouth.

"Blue team, forward!" she yelled.

Everyone shouted, shaking their swords, followed her and Tess into the south woods. Tess noticed Percy trying to talk to Annabeth, but didn't pay it any mind. They got to their spot by the creek and everyone ran off to their positions. Percy was left on guard duty.

Thessea and Luke were to flank the other team from behind and take their flag. Everyone in their group went on ahead and left Luke and Tess hanging.

"Did it hurt?" Luke asked.

"Did what hurt?"

"Knowing she died and there was nothing you could do. That her blood is on your hands?"

Thessea let out a sigh before turning to look into his crystal blue eyes.

"Luke, I don't know how many times I have to tell you I'm sorry. I tried my best to help her-"

"And it wasn't good enough! It should've been you that died! Not her!"

"She shouldn't have died trying to protect you! You weren't worth her death and you still aren't!" Tess snapped before catching up with the rest of her team.

* * *

Annabeth's plan worked, Clarisse came after Percy and that allowed for the blue team to sneak around the flank and take their flag. Everyone cheered and hoisted Luke up as the flag was now the Hermes' cabin's. The mood was quickly ruined by a deep growl. Upon the rock sat a Hellhound, a fat dog from the Fields of Punishment.

"Percy run!" Annabeth shouted, but the hound jumped over her and pounced on him.

Chiron spat something in Greek, asking for his bow and after the hound cut into his chest, it fell over dead. Arrows sticking through it's neck as if it were a bull's-eye.

Chiron said something about it being summoned from inside the camp, which caused every last person to shut up except for Clarisse who shouted that Percy did it.

"You're wounded," Annabeth told Percy. "Quick, get in the water."

Percy claimed he was okay just for Annabeth to tell him to get in the water to which he obeyed.

Thessea knew what was happening, already knowing of the waters abilities. The cuts on Percy's chest began to close up until there was nothing, not even a scar. She watched as his eyes were filled with energy and his body straightened.

Percy started to ramble, apologizing for nothing when he was interrupted by Annabeth pointing at his head. A glowing green trident hovered above his head.

"It is determined," Chiron spoke.

Thessea chuckled softly as Percy looked like a deer in headlights, "My father?"

"Poseidon," said Chiron. "Earthshaker, Stormbringer, Father of Horses. Hail, Perseus Jackson, Son of the Sea God."

* * *

Thessea sat with Grover, Chiron, and Percy discussing the prophecy he was given. Grover was already assigned to go on the quest.

"I'm going," Thessea stated, not looking for an argument.

"Thessea-"Chiron started.

"I have been here longer than anyone and I have never gone on a quest. All this training has to be for something."

"It's to help you to survive."

"I need something that tests me and this is it and surely being the daughter of Poseidon, Zeus will surely blame me also. If I don't show up with Percy, it'll look bad."

Chiron pondered this before nodding his head, "Another has volunteered if you'll accept her help."

"Who would be crazy enough to volunteer for this?" Percy asked.

Annabeth became visible beside Tess after removing her Yankees cap.

After settling on the four for the quest Chiron told them to get packing.

For once Tess had someone to share the cabin with. She lay on her bed and sighed.

"Think we'll make it?" She heard Percy ask from underneath her.

"We have too."

Percy digested what she said before responding.

"Good night Tess."

"Night Percy."

That night, both of them had the best night sleep they had in awhile.

**Well… That's all I can think of hehe. I don't plan on going through the whole book or the first five anyways. Next chapter will most likely be the end of the first book with some Thessea and Percy time as they bond more and then we'll jump right into The Lost Hero! *Dramatic music* Review, tell me your thoughts and what not.**


	3. Chapter III

**Same as before, I don't own anything except my OC; everything else belongs to Rick Riordan. Let's go!**

They did it. They returned the master bolt to Zeus, and returned to camp alive and in one piece. By then it was near the end of summer and many campers were packing to head home.

"We did it," Tess said to Annabeth before hugging her.

"First quest completed. After so long," Annabeth answered.

A pause was shared of the two just taking in the scenery of the camp. The place they call or called home.

"So I'm going home for the year."

Tess looked at her friend in shock.

"You're not mad are you?"

"Why in world would I be mad? I'm happy for you, really. I'll miss you though."

"I'll miss you too. We'll have to keep in touch."

The two girls chatted for a bit before Annabeth left to pack. The camp seemed still and at ease and for the first time in a while, Thessea smiled a genuine smile that hurt her cheeks. She had completed her first quest successfully, and she had a brother and a mother.

Her thoughts were rattled by shouts for help as a nymph was dragging Percy's body out of the woods. Thessea sprinted toward them and noticed how sickly he looked.

"Chiron!" She screamed.

Percy woke in the sick bay with Tess, Annabeth, Grover, and Chiron surrounding him. After receiving some ambrosia and nectar he began to explain what happened.

Annabeth was hurt after being told it was him, but soon masked it with a tough face. The face she got when formulating a plan.

"I'm not as surprised as I should be," Thessea said matter of fact. Every time Luke looked at her, it was a look as if he had something planned, but that's every kid of Hermes, but Luke's look was one filled with discuss and that she was something to be ridden of. Like there was a surprise and here it is. Wrapped with a bow.

Chiron and Percy argued about Kronos, the Prophecy, and Luke which Tess didn't want to hear. So instead, she decided to go for a swim, for old time sakes. Thessea floated until she heard Percy calling for her.

"What is it?" She asked.

"Just wanted to tell you I'm leaving camp for the year."

"Oh… Okay. Well it's been one heck of a ride huh?" She said awkwardly.

"You're staying here?"

"I have nowhere else to go," Tess said this as if it were obvious.

Percy hesitated before saying, "If you want, you could come with me, I'm sure mom would love to have you."

"Really?!"

"Technically it is your home too, so yes."

Tess looked into her brother's eyes, the same ones that mirrored hers and she hugged him. Percy was stunned at first, but hugged her back.

"I'll get packing."

Percy watched as Tess tried to suppress a smile as she walked to cabin three.

* * *

The car ride home was long and tortuous for both of them. Tess watched so many people walk and ride to get to where they're going.

"Always this many people up here?" She asked Percy who sat on her right.

"Yep," he answered.

"Wow."

Finally they had arrived at the apartment complex which Sally and Percy lived. Thessea stood behind him and waited. Sally opened the door alright and when she saw her son, she covered her mouth and tears started to pool in her eyes.

"Percy, I'm so proud of you," she kissed his cheek.

"Mom, there's someone I brought with me," Percy answered.

Thessea slowly moved from around the corner and stood awkwardly.

"Oh my- Thessea? That really you?" Sally looked as if she were about to faint.

"Uh, hi mom."

Sally yanked her into a hug and the warmth and love surrounded Tess. She didn't know how to fell at first. But quickly decided she liked it. Tears fought their way into her eyes as she held onto her mother. Tears began to pour and she wasn't sure why, but she cried long and hard, she didn't want to or mean to soak Sally's shirt, but apparently it didn't bother her. Sally just stroked her back telling her it's ok.

When Tess was done Sally looked at her and Percy.

"I'm so proud of you two, and I'm sure you're father is too," She cupped each of their cheeks. "Go get unpacked and settled in. We'll figure out where you'll sleep when it comes to it."

"I can just sleep on the couch," Tess suggested.

"Or you can take my bed," Percy said.

"I'm not gonna take your bed."

Percy shrugged and lugged his bag to his room.

Tess went sat on the couch and sat there, not knowing what to do.

"I'll get started on lunch," Sally said.

Strangely Tess found herself digging in her bag for one thing, her necklace. She strung the newest bed on and held it in the palm of her hand. Fourteen beads in all, twelve years of surviving, one from being claimed, and one from her first quest. She never really wore it, because she felt every time she put it on, she strapped a chain of guilt around her neck also, depriving someone from a few years that they could've gotten.

"That's a lot of beads."

Thessea watched Percy plop down next to her.

"Yea. I don't like to wear it, or I don't want people asking the same questions."

"Mind if I ask?" Percy cautiously asked.

Tess opened her mouth to reply, but was interrupted by their mother, saying the food was done.

"Blue, mac and cheese?" Tess asked. "And blue sweet tea? And blue cookies?"

Percy was already sharing himself a plate, seeing nothing wrong with it.

"We try to eat blue," Sally said.

Thessea gave them a weird look.

"Long story," Percy added, mouth full of food.

Thessea slowly sat down then looked at the food strangely. She then thought to herself, '_If I can take on monsters and gods, I can surely take on this…food.'_

Thessea took a small spoonful and put it in her mouth. It was good, everything was, even if it was blue. After finishing her plate, Percy began to tease her about it.

"Can't believe you were scared of blue food," Percy laughed.

"Food isn't normally blue, so excuse me," Tess pointed her spoon at him threateningly.

"You looked like you were gonna draw your sword."

Percy clutched his stomach while Tess glared at him.

"I'll draw it on you," Tess muttered.

"If I can beat the pig-headed war god, than I can surely beat you," Percy smirked.

"You needed my help with him if I remember correctly," Tess looked like she was going to jump across the table.

"Yes I know, couldn't have done it without you."

Thessea stared at him, not sure if he was serious or not.

"Can still beat you though," He grinned.

Tess groaned, " You cannot beat me."

"We'll just have to settle this."

Tess smirked at him and stood up, "Challenged accepted, brother."

Percy stuck out his hand and she shook it. The grinned at each other before Tess went to change.

* * *

Percy woke up to strange noises coming from the living room. Instinctly he grabbed Riptide and slowly walked towards the source. Tess laid on her back, sweating, breathing hard, and letting out series out grunts.

"..run... Run," she mumbled. "..Tha-"

Percy shook her awake causing her to sit up quickly.

"You were having a nightmare," Percy whispered.

Tess turned away from him, embarrassed.

"It's the same one," she replied.

Percy sat down next to her as she brought her knees up to her chest.

They sat in silence for a bit until Tess broke it.

"Few years ago, something happened at camp, something I will never forget. This was the year Annabeth and Luke came to camp. There was another girl with them-"

"Thalia," Percy answered.

Tess looked at him like she was about to burst into tears, "She wanted to ensure her friends safety, get them to camp alive and I wanted to help. Somewhere in the battle I got surrounded. I didn't know she was in trouble until I heard Annabeth and Luke scream her name, I tried to get to her, I did, but I couldn't. Just barely out of her reach and she was killed in front of my eyes and I couldn't do anything. Not a thing! You know how that feels when you train all your life and it still isn't enough?!"

Tess was up, pacing about, and tears were streaming down her face. Percy just listened, letting her get this off her chest.

"It crushes you," She whispered. "It takes a toll on your mentality. I couldn't sleep for a while. Her face still freshly implanted in my mind, and no matter how many times Chiron told me I did my best, it stung. That's one of the reasons I don't wear my necklace. Because why should I wear mine when Thalia doesn't have a chance to wear hers?"

Percy yanked her into a hug and just held her until she stopped crying. The both of them sat on the couch quietly until they fell asleep.

Sally found her kids asleep, leaning on one another. She smiled and enjoyed the moment before shaking their shoulders.

"Wake up you two," She said.

Slowly their eyes fluttered open and so did their mouths.

"Percy you drooled on me," Tess said as she looked at the huge wet spot on her shirt.

"Your hair was in my mouth," he retorted.

"I'm going to have to wash my hair in bleach now."

"Drama queen."

Tess stuck her tongue out at him before shuffling towards the bathroom.

Percy sat at the table, still wiping the sleep from his eyes.

"So what's the plan today mom?" he asked.

"I have to work today and then I am going to get you and your sister enrolled in school."

"You have to work?"

"Well it is Monday. That means it'll just be you and Tess."

"You're gonna leave me with her?"

"Yes. Here's 30 bucks, show her around, something."

Percy sighed and nodded.

After Sally left, the real fun began.

"What do you want to do?" Percy asked.

"Still up for the challenge?" Tess grinning.

"There's no place for us to do that?"

"Surely you most know a secluded place right?"

Percy thought for a bit, and she knew she had an answer when he smiled.

It was an abandoned pool, the walls somewhat collapsed and just old.

"You ready to lose?" Tess smiled.

"We'll see who the real loser is," Percy answered.

The siblings crawled through a small hole in the side and jumped into the empty pool. Percy uncapped Riptide and Thessea activated Tidalwave and the two took a ready stance. Without warning Tess swung at Percy who parried it and countered. He hit her with the flat of his blade and was going for another attack when she side stepped and pushed her blade against his.

"Hey!" a voice shouted.

A group of guys were watching in horror. They watched like the two were killing each other.

"Dudes, no need to kill each other, just put the weapons down."

Percy and Thessea looked at each other, unsure of what to do.

"Run?" Tess suggested.

"On three," Percy said. "One, two, three!"

The pair bolted up and out of the pool. Percy scrambled through the hole first, and Tess was almost through, but she was yanked back in by one of the guys.

"Let me go!" She hollered swinging her sword. Strangely the boy hissed in pain before he disappeared into gold dust. "Percy!"

Percy jumped back in sword in hand, and the twins stood back to back. The guys laughed at them evilly while their skins turned scaly and their eyes turned into slits.

The twins immediately attacked, dodging, and slashing as they moved like a well oiled machine. Soon they were surrounded and even covered by gold dust.

"Let's go," Percy said.

"Yea," Tess agreed.

* * *

The pair got along more and more and with each year their bond got stronger. They been on many quests and the last one was the biggest and they succeeded somehow. Thessea no longer slept or felt pain about Thalia seeing how she was still alive and now part of Artemis' hunters. Everything was normal, or as normal as it can get for a demi-god, until one day.

"You okay?" Tess asked Percy as she sat down next to him.

They sat in their spot on the surf, watching the waves. This is where they really talked. Where they would discuss issues and problems, and just made sure one another were ok.

"Yea I'm fine," he answered.

Thessea pursed her lips and looked at her brother; the years definitely took a toll on him. He looked more rugged and older than he was, but I guess she could the same about herself and her friends.

"What about you? And Nico?" he asked.

"I don't even know anymore, one minute he's great and the next he disappears. It's frustrating."

"Still disappearing? Thought he was over that?"

"Guess not…"

"What do you see in him?"

"There's something, he's different from everybody else."

"I mean he is Hades' son."

Tess playfully pushed Percy's shoulder, "Shut up."

They sat there for a while in comfortable silence, Tess leaning against him and Percy with his arm around her.

"Is it wrong I still think about Luke? And what he did?" Percy finally said.

"No. I still think about it now and again, but I try not to."

Thessea grabbed Percy's hand and squeezed it reassuringly.

"Think it's over?" Percy asked.

"We're demi-gods, it'll never be over, but for now it is."

Percy looked at his sister and then to the water. The both of them feel asleep leaning on each other, like they've done so many times before.

"Good night Perce," She whispered, already halfway into the void of sleep.

"Night Tess," Percy whispered back.

The next morning, Thessea found herself lying on the sand; she slowly looked around and didn't see her brother.

"Percy?" She called out, panic rising in her voice. Tess looked everywhere he could possibly be and more and still didn't find him. He was gone.


End file.
